Exposure system and production method for exposure system

ABSTRACT

The invention is directed to the provision of an exposure apparatus that can determine a correction value for each individual light-emitting part by employing a method that detects the amount of light corresponding to one particular light-emitting part from composite light containing light rays from adjacent light-emitting parts, and also to the provision of a method for producing such an exposure apparatus. The production method according to the invention comprises the steps of lighting a plurality of light-emitting parts at the same time, detecting an output light-amount distribution across all of the plurality of light-emitting parts by making measurements using a line-like light-receiving device, detecting a peak position corresponding to each light-emitting part by using the output light-amount distribution; detecting the amount of light of each light-emitting part based on the peak position, and determining, based on the amount of light of each light-emitting part, the correction value for correcting nonuniformity in the amount of light of the light-emitting part.

BACKGROUND ART

The present invention relates to an exposure apparatus in whichcorrection values are prestored, for correcting variations in the amountof light among a plurality of pixels contained in a light modulatingdevice, and a method for producing such an exposure apparatus.

DESCRIPTION OF THE PRIOR ART

It is known to provide an optical printer which forms a color image byexposing a color photosensitive material or the like to light by usingan exposure head equipped with a plurality of light-emitting parts. Assuch an exposure head has a plurality of light-emitting parts, there hasbeen the problem that variations occur in the amount of light among theplurality of light-emitting parts, resulting in an inability of obtainan image of good quality. To address this problem, it has been practicedto apply shading correction (light-amount correction) by detecting thevariations among the light-emitting parts.

In a first prior art method of shading correction, the amount of lightemitted from each light-emitting part is measured with a light sensor bylighting the plurality of light-emitting parts one at a time.

This method, however, has had the deficiency that a correct shadingcorrection cannot be accomplished because environmental conditions ofthe light-emitting parts and the light sensor vary during themeasurement. Another deficiency has been that it takes time to completethe measurement because the measurement is made on one light-emittingpart at a time. Furthermore, when the exposure head constructed from theplurality of light-emitting parts is actually operated for exposure,light rays from two or more light-emitting parts (for example, aplurality of adjacent light-emitting parts) are incident in overlappingfashion on any particular point on the photosensitive material due tothe spreading of light emitted from each light-emitting part and due tosuch errors as the tilting of a lens system (SELFOC lens array, etc.)provided between the light-emitting parts and the photosensitivematerial. Accordingly, when exposure is performed on the photosensitivematerial by using the exposure head which has been corrected forvariations in the amount of light among the light-emitting parts bymeasuring the amount of light emitted from one particular light-emittingpart, unevenness occurs in the amount of exposure of the photosensitivematerial because of the light spilling over from adjacent light-emittingparts, resulting in unevenness in color image density. That is, theabove method has had the further deficiency of being unable to make acorrection for the effects from the adjacent light-emitting parts.

In a second prior art method of shading correction, a trial exposure isperformed on a photosensitive material by lighting all of the pluralityof light-emitting parts at the same time, after which the photosensitivematerial is developed and color densities measured, and the variation inthe amount of light of each light-emitting part is corrected based onthe measured values of the color densities (Japanese Unexamined PatentPublication No. H09-127485, pp. 7-8 and FIG. 5(A)).

This method, however, has had the deficiencies that it takes time andlabor to develop the photosensitive material, and that the variation inthe amount of light of each light-emitting part cannot be correctedquickly and in a simple manner.

In a third prior art method of shading correction, the effects of lightfrom adjacent light-emitting parts are considered when correcting thevariation in the amount of light of each light-emitting part in anexposure head having a plurality of light-emitting parts (JapanesePatent No. 3269425). In this method, it is assumed that onelight-emitting part corresponds to one particular region on the lightreceiving surface, and the correction value for correcting the variationin the amount of light emitted from one light-emitting part isdetermined based on the amount of light received on that one region. Itis assumed here that the amount of light received on the one region isaffected by the light from three light-emitting parts, that is, theamount of light (Li, i) from the one light-emitting part correspondingto that one region and the amounts of light (Li−1, i) and (Li+1, i) fromits left and right adjacent light-emitting parts.

In this method, however, as the amount of light received on the oneregion includes the amounts of light (Li−1, i) and (Li+1, i) from theleft and right adjacent light-emitting parts as just described, therehas been the problem that, if the one light-emitting part correspondingto the one region is controlled, the unevenness in the amount of lightfalling on the photosensitive material cannot be corrected, resulting inunevenness in image density. There has also been the problem that ittakes time to complete the measurement, because the measurement cannotbe performed by lighting all of the plurality of light-emitting parts atthe same time.

SUMMARY OF THE INVENTION

With the first prior art method described above, it has basically notbeen possible to make a correct correction. With the second prior artmethod described above, while the correction can be made for the effectsof adjacent light at the same time, there has been the problem that thecorrection takes too much time and labor since it takes the steps ofexposure, development, and measurement. Further, the third prior artmethod described above aims at correcting for the effects of adjacentlight, but the method itself is wrong and a correct correction cannot bemade.

Accordingly, it is an object of the present invention to provide anexposure apparatus that can determine a correction value for eachindividual light-emitting part by employing a method that detects theamount of light corresponding to one particular light-emitting part fromcomposite light containing light rays from adjacent light-emittingparts, and a production method for producing such an exposure apparatus.

It is another object of the present invention to provide an exposureapparatus that can determine a correction value for each individuallight-emitting part by measuring the amount of light of each of theplurality of light-emitting parts in the exposure head under the sameconditions without causing changes in the environmental conditions ofthe light-emitting parts and the light sensor, and a production methodfor producing such an exposure apparatus.

It is a further object of the present invention to provide an exposureapparatus that can correct the amount of light of each of the pluralityof light-emitting parts in the exposure head in such a manner as not tocause nonuniformity in exposure due to light from adjacentlight-emitting parts, and a production method for producing such anexposure apparatus.

To achieve the above objects, there is provided, according to thepresent invention, a production method comprising the steps of lightingthe plurality of light-emitting parts at the same time, detecting anoutput light-amount distribution across all of the plurality oflight-emitting parts by making measurements using a line-likelight-receiving device, detecting a peak position corresponding to eachof the light-emitting parts by using the output light-amountdistribution, detecting the amount of light of each light-emitting partbased on the peak position, and determining, based on the amount oflight of each light-emitting part, a correction value for correctingnonuniformity in the amount of light of the light-emitting part. As thecorrection value for each individual light-emitting part can bedetermined by employing the method that detects the amount of lightcorresponding to one particular light-emitting part from composite lightcontaining light rays from adjacent light-emitting parts, a correctshading correction can be accomplished.

Preferably, in the production method according to the present invention,the step of determining the amount of light of each light-emitting partincludes the steps of obtaining a value corresponding to each peakposition in the output light-amount distribution, and determining thevalue as the amount of light of the light-emitting part.

Further preferably, in the production method according to the presentinvention, the step of determining the amount of light of eachlight-emitting part includes the steps of providing a referencelight-amount distribution, obtaining a sole light-amount distributionfor the light-emitting part corresponding to the peak position, by usingthe reference light-amount distribution and the output light-amountdistribution near the peak position, and determining the amount of lightof the light-emitting part based on the sole light-amount distribution.

Preferably, in the production method according to the present invention,the light-emitting parts each have an opening tilted at a prescribedangle in a direction in which the light-emitting parts are arranged.

Preferably, in the production method according to the present invention,the step of lighting the plurality of light-emitting parts at the sametime includes the steps of lighting all of odd-numbered ones of theplurality of light-emitting parts at the same time, and lighting all ofeven-numbered ones of the plurality of light-emitting parts at the sametime.

Preferably, in the production method according to the present invention,the step of detecting the output light-amount distribution includes thesteps of detecting a first output light-amount distribution occurringwhen all of the odd-numbered ones of the plurality of light-emittingparts are lighted at the same time, and detecting a second outputlight-amount distribution occurring when all of the even-numbered onesof the plurality of light-emitting parts are lighted at the same time.

Preferably, in the production method according to the present invention,the step of detecting the peak position includes the steps of detectinga first peak position by using the first output light-amountdistribution, detecting a second peak position by using the secondoutput light-amount distribution, and combining the first peak positionand the second peak position.

Preferably, in the production method according to the present invention,the control means has a memory, and is configured to control theexposure head based on data stored in the memory, wherein the methodfurther includes the step of storing the thus determined correctionvalue in the memory.

Preferably, in the production method according to the present invention,the light-receiving device includes light-receiving parts, each having awidth narrower than the width of each of the light-emitting parts.

Preferably, in the production method according to the present invention,the number of light-receiving parts contained in the light-receivingdevice is equal to an integral multiple of the number of the pluralityof light-emitting parts.

Preferably, in the production method according to the present invention,the light-receiving parts are arranged in such a manner that three ormore light-receiving parts correspond to one light-emitting part.

Preferably, in the production method according to the present invention,a light-receiving surface formed by the plurality of light-receivingparts is longer than a light-emitting surface formed by the plurality oflight-emitting parts.

Further, to achieve the above objects, there is provided, according tothe present invention, an exposure apparatus comprising an exposure headhaving a plurality of light-emitting parts whose amounts of light eachvary with a supplied driving signal, and a control means for generatingthe driving signal by correcting image data in accordance with acorrection value stored in a memory, wherein the correction value ispreferably determined based on the steps of lighting the plurality oflight-emitting parts at the same time, detecting an output light-amountdistribution across all of the plurality of light-emitting parts bymaking measurements using a line-like light-receiving device, detectinga peak position corresponding to each of the light-emitting parts byusing the output light-amount distribution, detecting the light of lightof each light-emitting part based on the peak position, and determining,based on the amount of light of each light-emitting part, the correctionvalue for correcting nonuniformity in the amount of light of thelight-emitting part.

To achieve the above objects, there is also provided, according to thepresent invention, a production method comprising the steps of lightingthe plurality of light-emitting parts at the same time, measuringamounts of light from the plurality of light-emitting parts by using alight-receiving device, detecting a peak value and a peak position frommeasured values obtained by the light-receiving device, and determining,based on the peak value and the peak position, a correction value forcorrecting nonuniformity in the amount of light emitted from eachlight-emitting part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing one example of a system accordingto the present invention.

FIG. 2 is a diagram showing an external view of the one example of thesystem according to the present invention.

FIG. 3 is a diagram for explaining a CCD line sensor used in the systemaccording to the present invention.

FIG. 4 is an exploded perspective view showing one example of anexposure head.

FIG. 5 is a cross-sectional view of the exposure head shown in FIG. 4.

FIG. 6 is a cross-sectional view showing one example of an exposureapparatus according to the present invention.

FIG. 7 is a perspective view of the exposure apparatus shown in FIG. 6.

FIG. 8 is a cross-sectional view of a liquid crystal shutter used in theexposure head shown in FIG. 4.

FIG. 9A is a diagram showing one example of the shape of openings in aliquid crystal shutter array, and FIG. 9B is a diagram showing anotherexample of the shape of openings in a liquid crystal shutter array.

FIG. 10 is a diagram for explaining a light path in the system.

FIG. 11 is a conceptual diagram showing one example of an exposurecontrol circuit.

FIG. 12 is a flowchart for correcting an applied electric current value.

FIG. 13 is a diagram showing one example of the distribution oflight-amount data detected by the CCD line sensor.

FIG. 14 is a diagram showing one example of the distribution of theamount of change between adjacent values.

FIG. 15 is a diagram showing one example of the distribution of theamount of light for each driving pixel.

FIG. 16 is a flowchart for obtaining correction values for shadingcorrection.

FIG. 17 is a diagram showing one example of the distribution ofcorrection reference values.

FIG. 18 is a diagram showing one example of the driving characteristicof driving pixels in the liquid crystal shutter array.

FIG. 19 is a diagram showing one example of the sensitivitycharacteristic of a photosensitive material.

FIG. 20 is a diagram showing the relationship between normalizedexposure light amount and normalized driving time for the driving pixelsin the liquid crystal shutter array.

FIG. 21 is a diagram showing one example of a relational equation.

FIG. 22 is a diagram showing, by way of example, correction valuesobtained in accordance with the flow of FIG. 16.

FIG. 23 is a diagram for explaining an advantage in obtaining thecorrection values by reference to Fmin.

FIG. 24 is a diagram showing one example of the result of the shadingcorrection performed using the correction values obtained in accordancewith the flow of FIG. 16.

FIG. 25 is a diagram showing a second processing flow for obtainingilluminance.

FIG. 26 is a diagram showing the relationships between weight functions,distribution of sole illuminance, and illuminance.

FIG. 27 is a diagram for explaining the relationships between thedriving pixels, light-receiving elements, and the illuminance of eachdriving pixel.

FIG. 28 is a diagram showing the relationship between an ideallight-amount distribution and a continuous light-amount distribution.

FIG. 29 is a diagram showing a second processing flow for obtaining peakvalues and peak positions.

FIG. 30A is a diagram showing the distribution of sole illuminance andthe continuous light-amount distribution for a liquid crystal shutterarray having openings of rectangular shape, and FIG. 30B is a diagramshowing the distribution of sole illuminance and the continuouslight-amount distribution for a liquid crystal shutter array havingopenings of parallelogrammic shape.

FIG. 31 is a diagram for explaining the characteristic of light-amountdata detected when the liquid crystal shutter array having openings of aparallelogrammic shape is used.

FIG. 32A is a diagram showing one example of light-amount data detectedwhen only odd-numbered pixels are driven, and FIG. 32B is a diagramshowing one example of light-amount data detected when onlyeven-numbered pixels are driven.

DETAILED DESCRIPTION OF THE INVENTION

A first embodiment according to the present invention will be describedbelow with reference to drawings.

FIG. 1 is a diagram showing an overview of a production system, and FIG.2 is a diagram for explaining an external view of the system.

As shown in FIGS. 1 and 2, the production system comprises an exposurehead 100 to be measured, a measuring apparatus 200, and a personalcomputer (hereinafter referred to as the PC) 300 for performing control.

The exposure head 100 is mounted on the measuring apparatus 200 using anattachment not shown, and a signal line 126 is connected to an interface(hereinafter referred to as the IF) 240 of the measuring apparatus 200.The measuring apparatus 200 and the PC 300 are interconnected by a busline 260 so that data can be transferred between them. Further, theexposure head 100 is connected to an exposure control circuit 150, whichtogether constitute an exposure apparatus 500.

As shown in FIG. 1, the measuring apparatus 200 includes a drivingcondition signal creating means 210, an electric current supply circuit220, the IF 240 for connecting with the exposure head 100, an IF 250 forconnecting with the PC 300, and a light-amount measuring means 270.

The driving condition signal creating means 210 includes a CPU 211 forcontrolling the entire operation, a liquid crystal shutter drivingcircuit 212, an LED driving condition storing memory 213 for storingcontrol condition data for LEDs contained in the exposure head 100, aliquid crystal shutter driving condition storing memory 214 for storingdriving condition data (such as driving grayscale data for each drivingpixel) for the measurement of a liquid crystal shutter array 118(described later) contained in the exposure head 100, a light-amountstoring memory 215 for storing the illuminance F(N) (described later) ofeach driving pixel of the liquid crystal shutter array 118, and acorrection value storing memory 216 for correcting the variation in theamount of light of each of the driving pixels in the liquid crystalshutter array 118.

The CPU 211 is connected via the IF 250 and the bus line 260 to the PC300, and receives control data from the PC 300 about the measurementstart timing, measurement end timing, driving conditions for theexposure head 100, etc. The CPU 211 controls the light-amountmeasurement (production/setting of the exposure apparatus) bycontrolling the exposure head 100, the measuring apparatus 200, etc. inaccordance with the received control data.

The liquid crystal shutter driving circuit 212 controls, via the IF 240and the line 126, the driving of the plurality of driving pixels of theliquid crystal shutter array 118 contained in the exposure head 100.

The electric current supply circuit 220 supplies electric current viathe IF 240 and the line 126 to the LEDs 120 (blue LED, green LED, andred LED) (described later) contained in the exposure head 100; theintensity of light emission of each LED can be controlled by varying thevalue of the electric current supplied.

The light-amount measuring means 270 includes a CCD line sensor 230, aCCD control circuit 276 for controlling the plurality of light-receivingelements contained in the CCD line sensor 230, a received light amountdetecting circuit 274 for detecting the amount of light received by eachindividual one of the plurality of light-receiving elements contained inthe CCD line sensor 230, and an integrator circuit 272 for obtainingreceived light-amount data per unit time by integrating the detectionoutput of the received light amount detecting circuit 274.

The electric current supply circuit 220 and the liquid crystal shutterdriving circuit 212 transmit an LED driving signal and a liquid crystalshutter driving signal via the IF 240 to drive the LEDs 120 and theliquid crystal shutter array 118, respectively.

The measuring apparatus 200 further includes a ROM for storing controlprograms of the CPU 211, a RAM for temporarily storing various kinds ofdata, and various kinds of signal lines and bus lines for transferringdata between the constituent elements.

The measuring apparatus 200 and the PC 300 obtain the LED drivingcondition data for the LEDS 120 and the shading correction value datafor the liquid crystal shutter array 118 in accordance with themeasuring procedures described later, and temporarily store the data inthe LED driving condition storing memory 213 and the correction valuestoring memory 216, respectively. The PC 300 transmits (as indicated by302) the LED driving condition data and the shading correction valuedata for the liquid crystal shutter array 118 to the exposure controlcircuit 150 in the exposure apparatus 500, and stores the data in an LEDdriving condition storing memory 160 (described later) and a correctionvalue storing memory 153 (described later), respectively, contained inthe exposure control circuit 150; the exposure apparatus 500 capable ofperforming proper LED driving and shading correction is thus produced.

Here, the LED driving condition data and the shading correction valuedata, measured by the measuring apparatus 200, may be stored in theexposure control circuit 150 as the measurements are made, as previouslydescribed. In that case, the LED driving condition storing memory 213and the correction value storing memory 216 in the measuring apparatus200 can be omitted.

Alternatively, the following procedure may be employed: (1) a pluralityof exposure heads are measured successively by also using the measuringapparatus 200, (2) LED driving condition data (electric current valuedata) and shading correction data for the plurality of exposure heads100 are temporarily stored in the PC 300, (3) the data are transferredor moved (via a medium such as an FD or a CD) to another PC, (4) theexposure heads are connected to the respective exposure controlcircuits, and (5) using that other PC, the data are recordedsuccessively in the respective exposure control circuits. In that case,it is preferable to identify each exposure head by using a serial numberprinted on a serial number sheet 132 described later.

FIG. 3 shows a schematic diagram of the CCD line sensor 230. The CCDline sensor 230 has 2048 vertically long light-receiving elements 232,each having a length “a” of 2500 μm and a width “c” of 25 μm, arrangedat a pitch “d” (25 μm). Therefore, in actuality, the light-receivingelements are very closely spaced together, leaving almost no gap betweenthem, but in FIG. 3, a gap is shown between each light-receiving elementfor convenience of explanation.

In FIG. 3 are also shown the driving pixels 234 of the liquid crystalshutter array 118 described later; the driving pixels 234 each have alength “b” of 150 μm (or 200 μm) and a width “e” of 76 μm, and arearranged at a pitch “f” (100 μm). Accordingly, the driving pixels 234are arranged so that four light-receiving elements 232 correspond to onedriving pixel. In the present embodiment, the liquid crystal shutterarray 118 has a total of 480 driving pixels, and the driving pixels 234are arranged in a straight line as shown in FIG. 3. However, the drivingpixels may be arranged in a staggered pattern, for example, to match thewiring layout of electrodes for driving the driving pixels.

Further, as shown in FIG. 3, the overall length of the light receivingsurface made up of the light-receiving elements is chosen to be longerthan the overall length of the light emitting surface made up of thedriving pixels.

In the present embodiment, the driving pixels 234 are arranged so thatfour light-receiving elements 232 correspond to one driving pixel, butthe arrangement is not limited to this particular example. For example,it is preferable that the number of light-receiving elements is equal toan integral multiple of the number of driving pixels, and thearrangement may be made so that three, five, or seven light-receivingelements correspond to one driving pixel. In particular, it ispreferable to arrange the driving pixels so that three or morelight-receiving elements correspond to one driving pixel.

Referring to FIGS. 4 and 5, a description will be given of theconstruction of the exposure head 100 used as the target to be measuredin the system according to the present invention. FIG. 4 is an explodedperspective view of the exposure head 100, and FIG. 5 is across-sectional view of the exposure head 100. As shown, the exposurehead 100 comprises an upper housing 104 and a lower housing 130 betweenwhich are arranged an upper reflective plate 106, a light guiding device108, a mirror 112, a lower reflective plate 114, a liquid crystalshutter array 118, and LEDS 120. The upper housing 104 and the lowerhousing 130 are fixed together by a clip 140 so as not to be separatedfrom each other.

A light shielding sheet 102 is attached to the upper surface of theupper housing 104 to block external light. Further, a serial numbersheet 132 for identifying the exposure head 100 and a driving key 136are attached to the lower surface of the lower housing in the figure,and a Selfoc lens array (registered trademark) 138 is fixed to a groovein the lower housing 130.

The upper reflective plate 106 is constructed so as to surround thelight guiding device 108 and to reflect the light from the LEDS 120 sothat the light can be selectively emitted from a protrusion 110 of thelight guiding device 108. The reflective mirror 112 reflects the lightfrom the LEDS 120 into the light guiding device 108, while a slit 116formed in the lower reflective plate 114 serves as an escape for theprotrusion 110 of the light guiding device 108. The liquid crystalshutter array 118 is positioned and fixed onto the lower housing 130,while adjusting the position of its light path, by adjusting screws 124and 126. The LEDs 120, the light source of the exposure head 100,consist of red, green, and blue LEDs. A signal line 122 for controllingthe driving time of each driving pixel in the liquid crystal shutterarray 118 and for applying an electric current to the LEDs 120 isconnected to the liquid crystal shutter array 118, and the other end ofthe signal line 122 is brought outside the exposure head 100 frombetween the upper and lower housings 104 and 130. Indicated at 128 inthe figure is a bearing for moving the exposure head 100. The drivingkey 136 is a member for determining the driving timing, etc. of theexposure head together with a sensor, etc. not shown when driving theexposure head 100 by means of a ballscrew not shown and the bearing 128.The selfoc lens array 138 is an optical device for forming an erectimage with unity magnification at the focus, and comprises a largenumber of cylindrical lenses arranged in overlapping fashion along thelongitudinal direction.

Further, as shown in FIG. 5, a scattering film 107 is formed on theupper surface of the light guiding device 108 in the figure, extendingalong the longitudinal direction of the light guiding device 108 inorder to concentrate the colored lights from the LEDs 120 in thedirection of the liquid crystal shutter array 118 disposed directlybelow the light guiding device 108 in the figure. The scattering film107 is formed by applying a white scattering substance in a straightline pattern. When the exposure head 100 is mounted on the measuringapparatus 200, the colored lights from the scattering film 107 arepassed through the liquid crystal shutter array 108 and the SELFOC lensarray 138, and focused on the CCD sensor array 230.

FIG. 6 shows a cross-sectional view of the exposure apparatus 500, andFIG. 7 shows a perspective view with an upper lid 15 removed. Theexposure apparatus 500 contains the exposure head 100 and the exposurecontrol circuit 150 in an outer case 1. The exposure head 100 and theexposure control circuit 150 are connected by the signal line 122. Theexposure control circuit 150 is fixed to the interior side of the outercase 1. With two bearing rods 128 passed through openings formed in thelower housing 130, the exposure head 100 is supported movably along thebearing rods 128.

A cassette 4 for holding recording media (print paper) 8 is providedbelow the outer case 1 in the figure in such a manner as to bedetachable (in the direction of arrow A).

The exposure head 100, while moving along the bearing rods 128, performsimage formation (for example, the formation of a latent image) on therecording media 8 held in the cassette 4.

The exposure apparatus 500 shown in FIGS. 6 and 7 is only an example,and the invention is not limited to the illustrated construction. Forexample, the exposure apparatus 500 may be constructed so that therecording medium 8 is moved while holding the exposure head 100 fixed.The cassette 4 may be provided separately from the exposure apparatus500. Further, the exposure apparatus 500 may be constructed byincorporating a processing unit for developing a latent image formed ona recording medium. Furthermore, the exposure apparatus 500 may beconstructed using only the exposure head 100 and the exposure controlcircuit 150.

FIG. 8 shows a cross-sectional view of the liquid crystal shutter array118 shown in FIGS. 4 and 5. In FIG. 8, a transparent common electrode411 made of a transparent ITO thin film or the like is formed over theentire lower surface of an upper substrate 401, and is covered with analignment film 413 of polyimide or the like. On the upper surface of alower substrate 402 are formed fine transparent pixel electrodes 416which are covered with an alignment film 415. The outer peripheries ofthe two substrates are bonded together with a seal member 403 formedfrom an epoxy resin or the like, and a liquid crystal 414 is sealedbetween the alignment films 413 and 415 formed on the respectivesubstrates. The thickness of the liquid crystal 414 is chosen to be 5μm. The transparent common electrode 411 is also covered with a lightblocking layer 412 formed from a chromium material or the like, and aslit is formed in the portion of the light blocking layer 412 whichcorresponds to the position of the transparent pixel electrode 416 sothat light can pass only through that portion. Polarizers 410 and 417are attached to the outside surfaces of the respective substrates. Theliquid crystal 414 operates, for example, in an STN mode with a twistangle of 240°, and the two polarizers 410 and 417 can be arranged withtheir polarization axes oriented relative to each other at an angle thatmatches the twist angle.

Further, the driving pixels 234, each formed between the transparentcommon electrode 412 and one of the transparent pixel electrodes 416,are arranged in a straight line to form the liquid crystal shutterarray. The driving pixels 234 forming the liquid crystal shutter arrayeach have a length (b) of 150 μm (or 200 μm) and a width (e) of 76 μm,and are arranged at a pitch (f) of 100 μm, as previously explained withreference to FIG. 3.

FIG. 9 is a diagram showing driving pixels in the liquid crystal shutterarray. FIG. 9A shows the liquid crystal shutter array described withreference to FIG. 3; as shown, the driving pixels 234 are rectangular inshape. The length “b” of each driving pixel 234 is 150 μm (or 200 μm),the width “e” is 76 μm, and the pitch “f” is 100 μm. FIG. 9B showsanother liquid crystal shutter array 118′. The example shown in FIG. 9Bhas openings 234′ tilted at a prescribed angle in the arrangementdirection of the driving pixels (hereinafter called the “tilted drivingpixels”). In FIG. 9B, the length “b” of each driving pixel 234′ is 150μm (or 200 μm), the width “e” is 76 μm, the pitch “f” is 100 μm, and thetilt θ is about 60°.

In the present embodiment, either liquid crystal shutter array can beused. However, when the tilted driving pixels are used, unexposedportions of the photosensitive material, which could arise due to gapsbetween the driving pixels, can be eliminated. Accordingly, when theliquid crystal shutter array 118′ having the tilted driving pixels 234′is used, it becomes possible to prevent vertical stripes from beingformed due to the unexposed portions remaining on the photosensitivematerial. However, as will be described later, when the tilted drivingpixels are used, the problem can arise that peak positions cannot bedetected distinctly when measuring the amounts of light.

Here, the tilt θ is preferably set in the range of 45° to 80° so thatthe gap between each driving pixel can be covered.

FIG. 10 is a diagram for explaining the light path leading from the LEDs120 contained in the exposure head 100 to the CCD line sensor 230. Asshown in FIG. 10, the light emitted from each LED 120 is introduced intothe light guiding device 108 along the longitudinal direction thereof,and is reflected downward by the scattering film 107 and directed towardthe liquid crystal shutter array 118 through the lower protrusion 110 ofthe light guiding device 108. The light passed through each drivingpixel 234 of the liquid crystal shutter array 118 in a controlled manneris focused on the CCD line sensor 230 through the SELFOC lens array 138.The exposure head 100 contains the LEDs of three colors, and the coloredlight emitted from each color LED is passed through the light path shownin FIG. 10 and focused on the CCD line sensor 230.

The exposure head 100 is designed so that the colored lights emittedfrom the respective color LEDs and emerging from the driving pixels 234of the liquid crystal shutter array 118 have equal amounts of light, butthere are cases where variations occur in the amount of light among theindividual driving pixels. The reason for this will be described, by wayof example, below.

First, the scattering film 107 is constructed to have a uniform widthalong the longitudinal direction of the light guiding device 108 inorder to uniformly project light from the lower protrusion 110 of thelight guiding device 108 toward the liquid crystal shutter array 118.However, it is difficult to form the scattering film 107 to have aperfectly uniform width along the longitudinal direction. As a result,subtle errors in the width of the scattering film 107 prevent the lightfrom uniformly entering the driving pixels of the liquid crystal shutterarray 118, and this causes random variations in the amount of lightamong the individual driving pixels.

Next, the driving pixels 234 of the liquid crystal shutter array 118 areformed so that the transmittance of each pixel varies in accordance withthe voltage applied across the transparent electrodes forming the pixel,thereby making it possible to control the transmittance. However, it isdifficult to make the light transmittance uniform across all the drivingpixels, in particular, when each driving pixel is opened. Accordingly,even when uniform light is introduced into all the driving pixels,variations occur in the amount of light among the individual drivingpixels.

Further, the light emerging from each driving pixel 234 of the liquidcrystal shutter array 118 is focused through the selfoc lens array 138which is constructed by arranging a large number of cylindrical lensesin overlapping fashion along the longitudinal direction. Accordingly,even when uniform light is introduced into the selfoc lens array 138,fluctuations occur in the emerging light corresponding with thearrangement cycle of the cylindrical lenses.

Because of the light-amount variations occurring among the individualdriving pixels for the above and other reasons, if an exposure isperformed on the photosensitive material by the exposure head 100, ithas not been possible to form images of good quality. Accordingly, itbecomes necessary to measure the amount of light of each driving pixel234 in the exposure head 100 and to apply a shading correction so thatan equal amount of light can always be obtained when data of the samegrayscale level is applied to any particular driving pixel 234.

FIG. 11 shows one example of the exposure control circuit 150. Theexposure control circuit 150 includes: an input IF 151 via whichgrayscale image data Dg is input from a personal computer or the like; ashading correction circuit 152 for applying a shading correction to thegrayscale image data Dg; a correction value storing memory 153 forstoring shading correction data which the shading correction circuit 152uses for shading correction; an LCS control circuit 154 which generatesa control signal (LCS control signal) for driving the liquid crystalshutter array 118 by using the corrected grayscale image data Dg′ andexposure timing data Sc; a look-up table (LUT) 155 which is used whengenerating the LCS control signal; and an LCS driving circuit 156 whichgenerates a driving signal (LCS driving signal) for actually drivingeach individual pixel of the liquid crystal shutter array in accordancewith the LCS control signal.

The exposure control circuit 150 further includes: an exposurecorrection circuit 158 which generates the exposure timing data Sc fromthe grayscale image data Dg; an LED lighting control circuit 159 whichgenerates an LED driving signal for driving the LEDs 120 in accordancewith the exposure timing data Sc and LED driving condition data; and anLED driving condition storing memory 160 for storing the LED drivingcondition data.

The LCS driving signal and the LED driving signal are transmitted to theexposure head via the signal line 122, and the liquid crystal shutterarray 188 and the LEDs 120 are driven in accordance with the LCS drivingsignal and the LED driving signal, respectively.

It is assumed here that the correction values for the shading correctionand the LED driving condition data (electric current value data),obtained as will be described later, are prestored in the correctionvalue storing memory 153 and the LED driving condition storing memory160, respectively.

Next, a description will be given of the operation for adjusting thevalue of the electric current to be applied to each LED and the methodof determining the illuminance of each driving pixel.

FIG. 12 shows a flow for correcting the value of the electric current tobe applied to each LED 120 of the exposure head 100. Prior to startingthe correction, the exposure head 100 to be measured is set in theprescribed position on the measuring apparatus 200, and the signal line122 is inserted in the IF 240. After that, the operator enters ameasurement start command on the PC 300, which is transmitted to the CPU211 of the measuring apparatus 200 via the bus line 260 to start themeasurement. Thereafter, the flow of FIG. 12 is carried out with the PC300 cooperating with the CPU 211 of the measuring apparatus 200 inaccordance with system control software stored in the PC 300.

First, a reference LED current of a predetermined value is applied fromthe electric current supply circuit 220 to a designated one of the LEDdevices 120 in the exposure head 100, and the designated LED device thusturns on (step 1201). The exposure head 100 of the present embodimenthas LED devices of three colors (blue, green, and red), and themeasurement is made for each color LED device. In the presentembodiment, when performing the measurement, the liquid crystal shutterdriving circuit 212 outputs an open control signal with a maximumdriving time (corresponding to the highest grayscale level) forapplication to all the driving pixels of the liquid crystal shutterarray 118. The control signal applied to each driving pixel during themeasurement need not necessarily be one corresponding to the maximumdriving time, but a control signal corresponding to an intermediatedriving grayscale level may be applied.

Next, the amount of received light from all the light-receiving elements232 of the CCD line sensor 230 is detected by the received light amountdetecting circuit 274, and integrated by the integrator circuit 272, andthe result is converted by an A/D conversion circuit not shown into adigital signal which is detected as light-amount data E(X) by the CPU211 (step 1202). In the present embodiment, as there are 2048light-receiving elements 232 as previously described, 2048 pieces oflight-amount data E(X) (X is 0 to 2047) are acquired. The distributionof the acquired light-amount data E(X) is shown in FIG. 13. As shown inFIG. 13, the light-amount data are shown as output values (0 to 4095) ofthe A/D conversion circuit.

Next, light-amount data Emax having the largest value is obtained fromamong the light-amount data E(X) of all the light-receiving elements(step 1203), and it is determined whether or not Emax lies within apredetermined range (step 1204). The reason for making thisdetermination is that, if Emax is large and the value exceeds the A/Dconversion limit of the A/D conversion circuit, the data afterconversion is highly likely to saturate, resulting in an inability toobtain a good measurement result. Conversely, if Emax is small, thismeans that the data is generally compressed, degrading the detectabilityof valleys, etc. to be described later, and a good measurement resultcannot be obtained. In the present embodiment, the setting is made sothat Emax lies within a range not higher than 90% but not lower than 80%of the A/D conversion limit.

If Emax is outside the predetermined range, the process proceeds to step1205 where the value of the reference LED current applied in step 1201is varied by a prescribed proportion, and the process from step 1202 to1204 is repeated. In the present embodiment, the prescribed proportionis 10%. The LED current value is reduced by 10% if Emax is higher thanthe upper limit of the predetermined range, and is increased by 10% ifEmax is lower than the lower limit of the predetermined range.

If LEDs of uniform quality can be obtained, for example, the above steps1201 to 1205 may be omitted.

If Emax is within the predetermined range, the process proceeds to step1206 where the position of each valley V(N) is detected from thedetected light-amount data E(X). As an example, the detected valleypositions are shown at 1201 in FIG. 13. Here, N is a serial numberindicating each valley, and is 0 or an integer not smaller than 1. Thevalleys V(N) appear at positions corresponding to those light-receivingelements 232 which are located at positions between the driving pixels234 and not directly below the driving pixels, as shown by Y₁ to Y₃ inFIG. 3. Accordingly, the positions of the driving pixels can beidentified by detecting the valleys V(N).

Next, a peak value P(N) between adjacent valleys V(N) and V(N+1) isdetected from the detected light-amount data E(X) (step 1207). As anexample, peak values are shown at 1202 in FIG. 13. At the same time, thepeak position Xp at which the peak value P(N) is detected, that is, thenumber of the light-receiving element from which the peak value P(N) isdetected, is obtained.

Next, the amount of change between adjacent values R(N), that is, theamount of change between the valley V(N) and its adjacent peak valueP(N), is detected (step 1208). The amount of change between adjacentvalues R(N) is obtained first between the valley V(N) and its adjacentpeak value P(N), and then between the peak value P(N) and its adjacentvalley V(N+1). As an example, the amount of change between adjacentvalues R(N) is shown in FIG. 14 for the case where the light-amount dataE(X) shown in FIG. 13 is detected. Here, N is a serial number indicatingthe amount of change between a particular pair of adjacent values, andis 0 or an integer not smaller than 1. In the illustrated example, thedirection in which the value rises from the valley V(N) to the adjacentpeak value P(N) is indicated by (+), and the direction in which thevalue falls from the peak value P(N) to the adjacent valley V(N+1) isindicated by (−).

Next, a maximum amount of increase, Rmax, and a maximum amount ofdecrease, Rmin, are obtained (step 1209). Rmin and Rmax are shown by wayof example in FIG. 14.

Then, by reference to the positions of Rmin and Rmax, the region betweenthem is recognized as the pixel region (step 1210). One example of thethus recognized pixel region (N=0 to 479) is shown in FIG. 15.

Next, five pixels are removed from each edge of the obtained pixelregion, and the remaining region is taken as the effective pixel region(step 1211). One example of the effective pixel region (N=5 to 474) isshown in FIG. 15. The pixels located at the edges of the liquid crystalshutter array 118 may have driving characteristics different from thoseof the driving pixels located in the center, due to such factors as thestructure of the liquid crystal shutter and the arrangement of thetransparent electrodes. Accordingly, five pixels at each edge are notused for image recording, and are therefore removed so that the lightamounts associated with such pixels will not be measured or stored. As aresult, the effective pixel region is N=5 to 474.

Next, the peak value P(N) contained in the effective pixel region istaken as the illuminance F(N) of the Nth driving pixel in the liquidcrystal shutter array 118 (480 pixels in the present embodiment), thatis, the amount of light emerging from that driving pixel (step 1212).

For the light-receiving elements located at the edges and outside theregion of the driving pixels 232 of the liquid crystal shutter array118, as shown in FIG. 3, the amount of received light decreasesdrastically; accordingly, the pixel positions are determined by assumingthat the first driving pixel (N=0) is located at the position (Rmax)where the amount of received light first rises abruptly, and that thelast driving pixel (N=479) is located at the position (Rmin) where theamount of received light abruptly falls at the end. The distribution ofthe illuminance F(N) obtained in the above procedure is shown in FIG.15. In FIG. 15, the distribution of the amount of light is shown bydrawing a curve in such a manner as to join the amounts of lightcorresponding to the respective driving pixels.

Next, a minimum light amount Fmin is detected from the illuminance F(N)within the effective pixel region (N=5 to 474) (step 1213), and it isdetermined whether or not Fmin lies within a predetermined light-amountrange (step 1214). Here, the value of Fmin is determined according tothe kind of the photosensitive material used with the exposure head 100;in particular, the brightness setting for the exposed image is takeninto account when determining the value.

If Fmin is outside the predetermined light-amount range, then in step1215 the value of the electric current being applied to the LED at thatinstant in time is varied by a prescribed proportion (5%), and thecurrent thus varied is applied to the LED from the electric currentsupply circuit 220, to acquire the light-amount data over again for eachlight-receiving element as in step 1202 (step 1216). Here, if Fmin islower than the lower limit of the predetermined range, the current valueis varied in a direction that increases the LED current; conversely, ifFmin is higher than the upper limit of the predetermined range, thecurrent value is varied in a direction that reduces the LED current.Thereafter, the process from step 1206 to step 1216 is repeated, and thevalue of the electric current applied to the LED is varied until Fminfalls within the predetermined light-amount range. In the above process,if Fmin is outside the predetermined range, the adjustment required hereshould normally be a fine adjustment, because control is alreadyperformed in accordance with the loop of steps 1202 to 1205 so that Emaxfalls within the predetermined range. However, if there is any dustadhering to the driving pixel corresponding to Fmin, or in the event offailure of the LED 120, an extensive adjustment procedure would berequired for bringing Fmin within the predetermined range (step 1215).In that case, it is preferable to not perform the Fmin adjustment stepbut to consider the exposure head 100 defective.

If, in step 1214, Fmin is within the predetermined light-amount range,the process proceeds to step 1217. In step 1217, the LED current valueat that instant in time is stored in the LED control condition storingmemory 213 and, at the same time, control data concerning the drivingtime of each driving pixel of the liquid crystal shutter array 118 atthat instant in time (the data defining the conditions for opening eachdriving pixel) is stored in the liquid crystal shutter driving conditionstoring memory 214.

Next, the illuminance F(N) at that instant in time is stored in thelight-amount storing memory 215 for the shading correction describedlater (step 1218), to complete the measurement of the amount of light ofeach driving pixel.

The illuminance (F(N), etc.) of each driving pixel 234 of the liquidcrystal shutter array 118, stored in the light-amount storing memory215, can be output from the PC 300 (displayed or printed) and used forvarious purposes. In the present embodiment, the light-amountmeasurement has been performed by setting the exposure head 100 to bemeasured onto the measuring apparatus 200, but alternatively, themeasuring apparatus may be incorporated into an image forming apparatushaving an exposure head.

As described above, as the light-receiving elements, each smaller inwidth than each driving pixel of the liquid crystal shutter array, arearranged so that a plurality of light-receiving elements correspond toone driving pixel, the amount of light can be measured by accounting forinteractions from a plurality of driving pixels, thus making it possibleto accurately measure the amount of light without using an imageactually formed on a photosensitive member.

Furthermore, as the amount light is not measured indirectly from thedensity of an image actually formed on a photosensitive material, but ismeasured by using the data acquired from the light-receiving elementsdisposed opposite the liquid crystal shutter array, the position of eachdriving pixel can be detected accurately, and the amount of light canthus be measured with higher accuracy.

Moreover, as the amount of light can be measured accurately withoutusing an image actually formed on a photosensitive material, the timefor developing the photosensitive material can be eliminated, making itpossible to measure the amount of light quickly.

A method for obtaining correction values for shading correction will bedescribed below.

FIG. 16 shows a flow for obtaining correction values for shadingcorrection by using the illuminance F(N) stored in the light-amountstoring memory 215 in step 1218 of FIG. 12.

In this case, P(N) is set equal to F(N) in step 1212 of FIG. 12. Thismeans that the peak value P(N) between the valleys V(N) of the detectedlight-amount data E(X) is used as a representative value of each drivingpixel and hence as the illuminance for the shading correction.

The flow of FIG. 16 may be carried out following the flow of FIG. 12,with the PC 300 cooperating with the CPU 211 of the measuring apparatus200 in accordance with the system control software stored in the PC 300,or may be carried out separately in the PC 300 alone.

First, a relational equation T(H) defining the relationship betweendriving grayscale (H) and normalized exposure illumination amount T,common to all the driving pixels of the liquid crystal shutter array118, is prepared (step 1601). The details of the relational equationT(H) will be described later.

Next, the illuminance values F(N) of all the driving pixels, measuredand stored in accordance with the flow of FIG. 12, are read out from thelight-amount storing memory 215 (step 1602).

Then, the minimum light amount Fmin is detected from among theilluminance values F(N) of the driving pixels (step 1603).

Next, N is set equal to 0, that is, the 0th driving pixel 234 isselected (step 1604).

Then, by reference to Fmin detected in step 1603, a correction referencevalue U(N) for the Nth driving pixel is obtained (step 1605). Here, U(N)can be obtained from the following equation.U(N)=Fmin/F(N)

Correction reference values U(N) are shown by way of example in FIG. 17for the case where the illuminance values F(N) shown in FIG. 15 are readout of the light-amount storing memory 215. The correction referencevalue for the pixel corresponding to the minimum light amount Fmin is1.00.

Next, H is set to 0, that is, the correction value for the drivinggrayscale level 0 is set (step 1606).

Next, the exposure illumination amount S(H) necessary when the drivinggrayscale level H is input is obtained for the Nth driving pixel fromthe correction reference value U(N) and the relational equation T(H) byusing the following equation (step 1607).S(H)=T(H)/U(N)

Next, a real number value H′ that satisfies S(H)=T(H′) is obtained forthe Nth driving pixel (step 1608). H′ represents the driving grayscalelevel that is necessary to obtain the same exposure illumination amountwhen the driving grayscale level H is given to the Nth driving pixel aswhen the driving grayscale level H is given to the driving pixelcorresponding to the minimum light amount Fmin. That is, the shadingcorrection is performed by changing H to H′ when the driving grayscalelevel H is given to the Nth driving pixel.

Next, a correction value H″ with an integer value is obtained byrounding H′ to the nearest integer (step 1609). This is because thesystem containing the exposure head 100 of the present embodiment canonly handle driving grayscale level data having an integer value 0 or 1to 255. Accordingly, this step can be omitted depending on thesituation.

Next, the correction value H″ obtained in step 1609 is stored in thecorrection value storing memory 216 (step 1610).

Thereafter, the same process (steps 1607 to 1611 and 1613) is repeatedfor the Nth driving pixel until the process is completed for all thedriving grayscale levels (0 to 255), and further, the same process asdescribed above (steps 1605 to 1614) is repeated for all the drivingpixels (N=0 to 479), after which the flow is terminated.

Here, T(H) is a relational equation that applies in common to all thedriving pixels of the liquid crystal shutter array 118, and defines therelationship between the driving grayscale (H) and the normalizedexposure illumination amount T. The relational equation T(H) is obtainedin advance according to the liquid crystal shutter array 118 used in theexposure head 100 and the photosensitive material used, from therelationship between the driving characteristic of the liquid crystalshutter array 118, shown in FIG. 18, and the sensitivity characteristicof the photosensitive material used, shown in FIG. 19.

The driving characteristic of the liquid crystal shutter array 118,shown in FIG. 18, depicts the relationship between the normalizedexposure illumination amount T and the driving time t (the time that thedriving pixel is opened to transmit light) for each driving pixel of theliquid crystal shutter array 118. The graph showing the drivingcharacteristic in FIG. 18 is not linear because the normalized exposureillumination amount T for each driving pixel of the liquid crystalshutter array 118 has the characteristic such as shown in FIG. 20 withrespect to the control signal for the driving pixel. More specifically,when the control signal is applied that opens the driving pixel at t₀and closes the driving pixel at t₁, the amount of exposure illuminationfrom the driving pixel of the liquid crystal shutter array does notinstantly rises to the maximum but gradually approaches the maximumexposure amount. In FIG. 20, graph E₁ shows the behavior of a pixellocated in the center portion (N=20 to 460) of the liquid crystalshutter array 118, while graph E₀ shows the behavior of a pixel locatedin an edge portion (N=0 to 19 or 461 to 479) of the liquid crystalshutter array 118. The behaviors of the liquid crystal pixels differbetween those located in the edge portions and those located in thecenter portion, because the driving pixels located in the edge portionsare close to the seal member 403; that is, it is believed thatimpurities, uncured resin, etc. resulting from the formation of the sealmember 403 made of resin affect the alignment film or the liquid crystallocated close to the seal member 403.

Usually, the difference between E₁ and E₀ is very small; therefore, agraph depicting the driving characteristic such as shown in FIG. 18 maybe obtained based only on E₁, and T(H) may be obtained based on thegraph. However, when a further detailed shading correction is desired,it is preferable to obtain in advance T₁(H) based on E₁ and T₀(H) basedon E₀ and to select the appropriate relational equation for use inaccordance with the number or the position of each driving pixel.

On the other hand, the sensitivity characteristic of the photosensitivematerial, shown in FIG. 19, represents the relationship between thedensity D and exposure amount E on the photosensitive material, wherethe density D corresponds to the grayscale level and the exposure amountE corresponds to the exposure illumination amount.

In the present embodiment, a unique relational equation T(H) definingthe relationship between the grayscale level data H and the normalizedexposure illumination amount T is obtained from the graphs shown inFIGS. 18 and 19; to facilitate the calculation in the subsequent step,the relational equation is expressed by the following 10th degreepolynomial by using a least squares approximation method.[MATHEMATICAL 1]${T(H)} = {{\sum\limits_{i = 0}^{10}\quad{A_{i}H^{i}}} = {A_{0} + {A_{1} \cdot H} + {A_{2} \cdot H^{2}} + {A_{3} \cdot H^{3}} + {A_{4} \cdot H^{4}} + {A_{5} \cdot H^{5}} + {A_{6} \cdot H^{6}} + {A_{7} \cdot H^{7}} + {A_{8} \cdot H^{8}} + A_{9} + H^{9} + {A_{10} \cdot H^{10}}}}$

Here, the coefficients A₀ to A₁₀ in the equation have the values shownin Table 1 below for the respective color LEDs. TABLE 1 Coefficient RedGreen Blue A₀ =   1.70162E−05 −1.77629E−05 −2.22264E−05 A₁ = 0.000121884  0.003690198   0.002519878 A₂ =   3.02639E−05 −0.000354631 −0.000219781A₃ = −2.40994E−06   1.55701E−05   1.10647E−05 A₄ =   1.07437E−07−3.26235E−07 −2.74451E−07 A₅ = −2.13617E−09   3.95078E−09   3.89363E−09A₆ =   2.28938E−11 −2.94641E−11 −3.36148E−11 A₇ = −1.42627E−13  1.37082E−13   1.79632E−13 A₈ =   5.18871E−16 −3.86408E−16 −5.79815E−16A₉ = −1.02478E−18   6.00614E−19   1.03472E−18 A₁₀ =   8.50283E−22−3.91608E−22 −7.82463E−22

In the present embodiment, T(H) has been obtained using the 10th degreepolynomial as described above, but the relational equation is notlimited to the 10th degree polynomial. However, since thecharacteristics shown in FIGS. 18 and 19 are nonlinear, it is preferableto approximate the relation by using a relational equation of degree 3or higher.

FIG. 21 shows examples of T(H), S(H), etc. described above. As shown inFIG. 21, since U(N)=1.00 for the driving pixel corresponding to Fmin, itfollows that S(H)=T(H), and the normalized driving time corresponding tothe highest grayscale level 255 is 1.00, which is the maximum exposureillumination amount. For a driving pixel whose amount of light is higherthan Fmin, when the same grayscale level H₁ is given, the exposureamount required is S(H₁), and the driving grayscale for obtaining thesame exposure amount is therefore H₁′. That is, when the drivinggrayscale H₁ is given to the applicable driving pixel, the shadingcorrection is applied so as to correct the grayscale to H₁′.

Correction values obtained in this manner are shown by way of example inFIG. 22. In FIG. 22, corrected driving grayscales corresponding to allthe driving grayscale levels given are shown for each driving pixel N.In the example of FIG. 22, the 123rd pixel is shown as the driving pixelcorresponding to Fmin. The example of FIG. 22 shows the correctionvalues for only the red LED device, but in actuality, correction valuesare also obtained in accordance with a similar procedure for the blueand green LED devices, and stored in the correction value storingmemory.

As earlier described, the correction values (see FIG. 22) obtained inaccordance with the flow of FIG. 16 are stored in the designatedmemories, such as the correction value storing memory 153 and the LEDdriving condition storing memory 163, provided in the exposure controlcircuit 150 connected to the exposure head 100. Here, the correctionvalues may be written to a recording medium such as an FD or CD togetherwith the electric current values obtained in the flow of FIG. 12 for therespective color LEDs, and the recording medium may be shipped with theexposure head 100 thus measured.

Next, the reason for obtaining the correction values by reference to theminimum light amount Fmin will be described briefly with reference toFIG. 23. Fmin is chosen as the reference in order to effectively utilizethe full range of the driving grayscale. For example, when Fmin is setas the reference, the driving pixel having the lowest exposureillumination amount is the driving pixel corresponding to Fmin; if thehighest grayscale level 255 is given to that driving pixel, thecorrection value is also 255. However, if the correction reference valuewere to be obtained for each driving pixel by reference to the maximumlight amount Fmax, the reference correction value U(N)=1.00 would haveto be mapped to the maximum light amount Fmax, and hence Smax(H)=T(H)for the driving pixel corresponding to Fmax. Here, if the driving pixelcorresponding to Fmax were set so as to provide the maximum normalizedexposure illumination amount (1.00) at the highest grayscale level 255(see Smax(H)), then when the highest driving grayscale (255) was givento the driving pixel corresponding to Fmin, a correction would have tobe made so that an amount of light higher than Fmax would be obtained.In that case, as shown in FIG. 23, to obtain the maximum normalizedexposure illumination amount required, a correction would have to bemade so as to provide a driving grayscale H₂ which is higher than thehighest grayscale level 255 (see Smin(H)). However, correcting thedriving grayscale to the level higher than the highest grayscale level255 is not possible.

One way to circumvent this would be to predefine the relational equationwith some margin so that the driving pixel corresponding to Fmax wouldprovide the maximum normalized exposure illumination amount at a drivinggrayscale level H₃ lower than the highest grayscale level 255 (seeSmax′(H)). However, differences in the amount of light, occurring in arandom manner among the driving pixels, cannot be predicted accurately.Here, if the corrected relational equation for the driving pixelcorresponding to the minimum light amount Fmin were set as Smin′(H), forexample, as shown in FIG. 23, then when the driving grayscale level H₃was given to that driving pixel, the grayscale level would only becorrected to H₄. Therefore, the full range up to the highest grayscalelevel 255 could not be made use of (see Smin′(H)).

By contrast, in the case of correcting the correction value by referenceto the minimum light amount Fmin, as the driving pixel corresponding tothe minimum light amount Fmin can be set to provide the maximumnormalized exposure illumination amount at the highest grayscale level,it becomes possible to make effective use of the full range of thedriving grayscale.

FIG. 24 shows one example of the result of the shading correction thathas been performed using the correction values obtained in accordancewith the flow of FIG. 16. FIG. 24 shows the distribution of the amountof light with the amount of light of each driving pixel expressed interms of an error (%) relative to the minimum light amount Fmin.

In the illustrated example, the red LED in the exposure head 100 wasturned on by applying the LED current obtained in accordance with theflow of FIG. 12, and the highest grayscale level data (255) was given toall the driving pixels; then, driving correction control was performedusing the correction values shown in FIG. 22, and the amounts of lightwere measured again in accordance with the flow of FIG. 12. As shown,the error among the amounts of light of the 480 driving pixels was 0.04%at maximum, which means that the error was corrected to the level thatdoes not affect the image formation at all.

Here, the relationship between the contents of the flowchart shown inFIG. 12 and the embodiments described hereinafter will be summarized.Steps 1206 and 1207 correspond to a peak detection process (A) in whichthe peak value (maximum value) and the valley (minimum value) occurringin correspondence with particular pixels and the positions of theiroccurrences (the numbers of the light-receiving elements) are detectedbased on the light-amount data E(X), in order to determine thecorrespondences between the pixels and the light-receiving elements. Thepeak detection process (A) is carried out by one of two methods, themethod explained in the description of the first embodiment or themethod that will be explained in the third embodiment to be describedlater; for example, when the driving pixels have a tilted shape as willbe described later, the peak value can be detected easily by employingthe method explained in the third embodiment.

Steps 1208 to 1211 correspond to an effective pixel region determiningprocess (B) in which, out of the driving pixels arranged in a line, thepixel region effective in determining the correction values isdetermined based on the peak values and valleys detected in the peakdetection process.

Step 1212 corresponds to an illuminance determining process (C) fordetermining the illuminance of each driving pixel contained in theeffective pixel region. The illuminance determining process (C) iscarried out by one of two methods, the method that takes the peak valueP(N) as representing the illuminance (F(N)) of the driving pixel asexplained in the description of the first embodiment or the method thatwill be explained in the second embodiment hereinafter described; inparticular, if the method explained in the second embodiment isemployed, the illuminance (F′(N)) of each driving pixel can be obtainedwith higher accuracy.

Next, the second embodiment will be described.

In the second embodiment, correction values for shading correction areobtained by using the illuminance F′(N) of each driving pixel that hasbeen determined using a method different from the method used todetermine the illuminance F(N) in the flow of FIG. 12. The flow afterF′(N) has been obtained by the method hereinafter described is the sameas the corresponding flow shown in FIG. 16, except that F(N) is replacedby F′(N).

In the process hereinafter described, the peak position Xp that yieldsthe peak value P(N) between the valleys V(N) in the detectedlight-amount data E(X) is taken as the representative position of eachdriving pixel and, using a weight function W(X), F′(N) is obtained andused as the illuminance for the shading correction.

As previously described, in the flow of FIG. 16, P(N) has been taken asrepresenting the illuminance F(N) of each driving pixel. This meansthat, as a plurality of light-receiving elements correspond to onedriving pixel, the measured value of the light-receiving elementexhibiting the peak value is regarded as representing the amount oflight of the driving pixel. In reality, however, light rays from aplurality of driving pixels are incident in overlapping fashion on theplurality of light-receiving elements, and the peak value may not alwayscoincide with the amount light of the particular one driving pixel. Inview of this, in the present embodiment, the illuminance F′(N) of theone particular driving pixel is determined, by using the weight functionW(x), from the detected light-amount data E(X) obtained from thelight-receiving elements (X is 0 to 2047). That is, as the detectedlight-amount data E(X) represents a mixture of light rays incident froma plurality of driving pixels, the illuminance of the one particulardriving pixel is estimated using the weight function W(X). Once theilluminance F′(N) of each driving pixel is estimated, optimum shadingcorrection can be performed by properly controlling each driving pixel.

Next, referring to FIG. 28, a description will be given of how theweight function W(X) is obtained. In FIG. 28, (N−1), (N), and (N+1)indicate three driving pixels in the liquid crystal shutter array 118,E(X−6) to E(X+6) indicate the (combined) light-amount data of the 13light-receiving elements in the CCD sensor array 230 that correspond tothe three driving pixels, and (X−6) to (X+6) indicate the positions ofthe respective light-receiving elements. In FIG. 28, it is assumed thatthe driving pixels (N−1) to (N+1) are ideal ones with no variations inthe light-amount distribution. The light-amount data E(X−6) to E(X+6)are shown by unfilled bars in the bar graph. In the illustrated example,the peak value P(N) corresponding to the pixel N−1 corresponds to thelight-receiving element X−4; likewise, the light-receiving element X±0corresponds to the driving pixel N, and the light-receiving element X+4to the driving pixel N+1.

As the driving pixels N−1, N, and N+1 are arranged close to each other,the amount of light received by the light-receiving element X±0 when allthe driving pixels are open is detected as the (combined) light amountE(X), combining the light amount from the driving pixel N−1, the lightamount from the driving pixel N, and the light amount from the drivingpixel N+1.

Here, attention was paid to one particular driving pixel N, and only thedriving pixel N was opened and the other driving pixels closed, thusallowing light to pass through only the driving pixel N while preventinglight from passing through the other driving pixels; in this condition,the light amounts G(N, X−6) through G(N, X±0) to G(N, X+6) detected bythe respective light-receiving elements (X) were obtained and plottedusing obliquely hatched bars in the bar graph.

Then, the ratios of the light amounts G(N, X−6) to G(N, X+6) to thelight amounts E(X−6) to E(X+6) corresponding to the respectivelight-receiving elements (X−6 to X+6) were calculated, and each ratiowas taken as the weight function W(X). Specific numeric values are shownin Table 2.

Using this weight function, the amount of the light incident only fromone particular driving pixel disposed directly above eachlight-receiving element can be accurately obtained from the combinedlight amount detected as the sum of the amount of the light incidentfrom the driving pixel disposed directly above the light-receivingelement and the amount of the light incident from the driving pixelsadjacent to that driving pixel. TABLE 2 Position of element W(X) (ratio)X − 6 0.009 X − 5 0.011 X − 4 0.018 X − 3 0.071 X − 2 0.487 X − 1 0.906X ± 0 0.954 X + 1 0.906 X + 2 0.487 X + 3 0.072 X + 4 0.018 X + 5 0.011X + 6 0.009

FIG. 25 shows a flow for obtaining the illuminance F′(N) of each drivingpixel (N is 5 to 474). The flow of FIG. 25 is one that replaces the step1212 in the flow of FIG. 12; the other steps are exactly the same asthose shown in FIG. 12.

After step 1213 in FIG. 12, the net illuminance G(N, X) of the drivingpixel N corresponding to the peak value P(N) is obtained by using theweight function W(X) and the detected light-amount data E(X) near theposition X of the light-receiving element from which the peak value P(N)was detected (step 2501).

Next, the net illuminance G(N, X) is integrated to obtain theilluminance F′(N) of the driving pixel N (step 2502).

Thereafter, the process returns to FIG. 12 and proceeds to step 1213,and the finally obtained illuminance F′(N) is stored in the light-amountstoring memory 215 (step 1218). After that, the process proceeds to theflow of FIG. 16 where the shading correction value is obtained based onthe illuminance F′(N).

In the second embodiment, after obtaining the light-amount data E(X)again in step 1216, the process may proceed directly to step 1212without returning to step 1206, as shown by the dashed line 1219 in FIG.12.

This is because, even if the LED current value is changed in step 1215,the peak position X does not change. Accordingly, as shown by the dashedline 1219, the previously detected peak position is used as-is in thepeak detection process (A) and the effective pixel region determiningprocess (B).

FIG. 26 shows the relationships of the positions of the light-receivingelements (937 to 953), the (combined) light-amount data E(X) detected bythe respective light-receiving elements, and the net illuminance G(X, N)hereinafter described.

The (combined) light-amount data E(937) to E(953) are shown by unfilledbars in the bar graph (some of the designations are omitted). In theillustrated example, the peak value P(225) corresponding to the drivingpixel 225 corresponds to the light-receiving element 939; likewise, thelight-receiving element 943 corresponds to the driving pixel 226, thelight-receiving element 947 to the driving pixel 227, and thelight-receiving element 950 to the driving pixel 228.

Here, attention was paid to one particular driving pixel 227, and thenet illuminances G(227, 941) to G(227, 953) incident on the respectivelight-receiving elements (941 to 953) through this particular drivingpixel 227 were obtained and plotted using obliquely hatched bars in thebar graph.

The method of obtaining the net illuminances G is as follows: the lightamount E(947) of the light-receiving element (947) corresponding to thepeak value P(227) of the driving pixel 227 and the light amounts E(941)to E(946) and E(948) to E(953) of the light-receiving elements (a totalof six light-receiving elements on both sides of 947) adjacent to theleft and right of the light-receiving element (947) are respectivelymultiplied by their corresponding weight functions W(X−6) to W(X+6), toextract only the net illuminances G(227, 941) to G(227, 953) presumed tobe incident on the respective light-receiving elements (941 to 953)through the driving pixel 227. In the present embodiment, almost all thelight emerging from the driving pixel 227 has successfully beenextracted by calculating it based on the light amounts obtained from thelight-receiving elements (945 to 949) located substantially directlyabove the driving pixel 227 and on the light amounts obtained from thelight-receiving elements (941 to 944) and (950 to 953) locatedsubstantially directly above the respective driving pixels 226 and 228on both sides of the driving pixel 227. The illuminance F′(227) shown inFIG. 27 is obtained by integrating the net illuminances G(227, 941) toG(227, 953).

The step 1212 “OBTAIN ILLUMINANCE F(N) OF EACH DRIVING PIXEL” in FIG. 12is accomplished by the above method.

In the present embodiment, the light-receiving elements 941 to 953 havebeen chosen as the extraction targets to extract the illuminancecorresponding to the driving pixel 227, but the range over which tochoose the extraction targets can be determined appropriately byconsidering the distances between the respective driving pixels, etc.

FIG. 27 shows the relationship between the illuminance F′(N)corresponding to each driving pixel and the peak position. In thefigure, illuminances F′(224) to F′(229) corresponding to the 224th to229th driving pixels are shown. FIG. 27 also shows how the light fromeach driving pixel 234 of the liquid crystal shutter array 118 reachesthe CCD sensor array 230 by passing through the SELFOC lens array 138.Due to the tilting, etc. of the microlenses forming the selfoc lensarray, the light from each driving pixel of the liquid crystal shutterarray 118 may not propagate in a straight line but propagate obliquely.Accordingly, the peak positions (each shown by an unfilled circle in thefigure) at which the peak light amounts P(N) are detected by the CCDsensor array 230 may not always be at equally spaced intervals.

As described above, in the second embodiment, the net illuminance G(N,X) is obtained from the peak position of each driving pixel N, thelight-amount data E(X) near the peak position, and the weight functionW(X), and the illuminance F′(N) of each driving pixel N is obtained fromthe net illuminance G(N, X). Since almost all the amount of the lightemerging from one particular driving pixel N can be extracted using thenet illuminance G(N, X), correct shading correction can be performed bycorrecting the illuminance F′(N). Accordingly, even if there arevariations in the peak positions in the light-amount distribution amongthe driving pixels of the liquid crystal shutter array 118, thecorrection value for the shading correction can be accurately obtainedfor each driving pixel.

Next, the third embodiment will be described.

In the third embodiment, the liquid crystal shutter array 118′ havingthe tilted driving pixels 234′ previously shown in FIG. 9B is used, andcorrection values for shading correction are obtained using the peakvalue P′(N) and its corresponding peak position Xp′ that have beendetermined using a method different from that used in the flow of FIG.12. The flow after the value P′(N) and Xp′ have been obtained by themethod described hereinafter is the same as the flows shown in FIGS. 12and 16, except that the value P(N) and Xp are replaced by P′(N) and Xp′,respectively. Further, after obtaining P′(N) and Xp′ by the followingmethod, the correction value for the shading correction may be obtainedby obtaining F′(N) in accordance with the flow shown in FIG. 25.

FIG. 29 shows the flow for obtaining the peak value P′(N) and itscorresponding peak position Xp′. The flow of FIG. 29 is one thatreplaces the steps 1206 and 1207 in the flow of FIG. 12; the other stepsare exactly the same as those shown in FIG. 12.

An example of the use of the liquid crystal shutter array 118′ havingthe tilted driving pixels 234′ shown in FIG. 9B will be described. FIG.30A shows the relationship between the ideal light-amount distribution Land the continuous illuminance distribution M when the liquid crystalshutter array 118 having the rectangular driving pixels 234 shown inFIG. 9A is used. On the other hand, FIG. 30B shows the relationshipbetween the ideal light-amount distribution L′ and the continuousilluminance distribution M′ when the liquid crystal shutter array 118′having the tilted driving pixels 234′ is used.

As shown in FIG. 30B, when the tilted driving pixels are used, the baseof the net illuminance distribution L′ spreads out, and the variation ofthe continuous illuminance distribution M′ can be reduced (can be madeflatter). Accordingly, when the tilted driving pixels are used,unexposed portions of the photosensitive material, which could arise dueto gaps between the driving pixels, can be reduced, making it possibleto prevent vertical stripes from being formed due to the unexposedportions remaining on the photosensitive material.

However, when the liquid crystal shutter array 118′ having the tilteddriving pixels 234′ is used, portions where the valley-peak differenceis extremely small can occur in the light-amount data detected by theCCD line sensor 230, and the valley V(N) may not be detected accurately(see step 1206 in FIG. 12). One example of such a situation is shown inFIG. 31. In FIG. 31, reference numeral 3201 shows one example of thelight-amount data (corresponding to E(X) in FIG. 13) detected when theliquid crystal shutter array 118′ having the tilted driving pixels 234′is used. In the center portion 3202 shown in enlarged form in FIG. 31,the valley-peak difference is so small that the valley V(N) cannot bedetected accurately. This is presumably because the valley that shouldappear at the position indicated by 3203 has been buried in light amountvariations occurring before and after it. If the valley V(N) cannot bedetected accurately, the peak value P(N) and the peak position Xp atwhich the peak value occurs cannot be obtained accurately.

In view of this, the third embodiment provides the method shown in FIG.29 in which only the odd-numbered or even-numbered driving pixels in theliquid crystal shutter array 118′ are driven in order to accuratelylocate the valley, the peak value, and the peak position. FIG. 32A showsthe light-amount data 3302 (Eo(X)) detected when only the odd-numbereddriving pixels in the liquid crystal shutter array 118′ are driven.Similarly, FIG. 32B shows the light-amount data 3304 (Ee(X)) detectedwhen only the even-numbered driving pixels in the liquid crystal shutterarray 118′ are driven. In the figure, the portions indicated by 3301 and3303 each correspond to the portion 3203 in FIG. 32, and 3201 indicatesthe detected light-amount data depicted in FIG. 31.

As shown in FIGS. 32A and 32B, when only the odd-numbered oreven-numbered driving pixels are driven, as the light amounts from bothsides of each driving pixel are disregarded, the valley-peak differenceincreases, so that the valley V(N) can be accurately located.

The flow of FIG. 29 will be described below. This flow corresponds tothe peak detection process (A) in FIG. 12.

In the present embodiment, when Emax is within the predetermined rangein step 1204, in FIG. 12, the process proceeds to step 3001 in FIG. 29.The liquid crystal shutter driving circuit 212 sends an open controlsignal to the liquid crystal shutter array 118′ so that, of all thedriving pixels, only the odd-numbered driving pixels will be opened forthe duration of a maximum driving time (corresponding to the highestgrayscale level) (step 3001). As previously explained with reference toFIG. 12, the open control signal applied to the driving pixels need notnecessarily be one corresponding to the maximum driving time, but acontrol signal corresponding to an intermediate driving grayscale levelmay be applied.

Next, the light-amount data Eo(X), detected by each light-receivingelement 232 when only the odd-numbered driving pixels in the liquidcrystal shutter array 118′ are opened, is acquired (refer to 3302 inFIG. 32A) (step 3002).

Next, the position Vo(No) of each valley is detected from thelight-amount data Eo(X) (step 3003). The method of obtaining each valleyfrom the light-amount data is the same as that shown in step 1206 inFIG. 12.

Next, the peak value Po(No) between the adjacent valleys Vo(NO) andVo(No+1) and the position Xpo (corresponding to the number of thecorresponding light-receiving element 232) at which the peak valuePo(No) is obtained are acquired (step 3004). The method of obtaining thepeak value between the adjacent valleys and the peak position is thesame as that shown in step 1207 in FIG. 12.

Next, the liquid crystal shutter driving circuit 212 sends an opencontrol signal to the liquid crystal shutter array 118′ so that, of allthe driving pixels, only the even-numbered driving pixels will be openedfor the duration of a maximum driving time (corresponding to the highestgrayscale level) (step 3005).

Next, the light-amount data Ee(X), detected by each light-receivingelement 232 when only the even-numbered driving pixels in the liquidcrystal shutter array 118′ are opened, is acquired (refer to 3304 inFIG. 32B) (step 3006).

Next, the position Ve(Ne) of each valley is detected from thelight-amount data Ee(X) (step 3007). The method of obtaining each valleyfrom the light-amount data is the same as that shown in step 1206 inFIG. 12.

Next, the peak value Pe(Ne) between the adjacent valleys Ve(Ne) andVe(Ne+1) and the position Xpe (corresponding to the number of thecorresponding light-receiving element 232) at which the peak valuePe(Ne) is obtained are acquired (step 3008). The method of obtaining thepeak value between the adjacent valleys and the peak position is thesame as that shown in step 1207 in FIG. 12.

Next, the peak values Po(No) corresponding to the odd-numbered drivingpixels and the peak values Pe(Ne) corresponding to the even-numbereddriving pixels are combined in alternating fashion, to acquire the peakvalues P′(N) corresponding to all the driving pixels (N is 5 to 474).Likewise, the peak positions Xpo, at which the peak values Po(No)corresponding to the odd-numbered driving pixels are respectivelyobtained, and the peak positions Xpe, at which the peak values Pe(Ne)corresponding to the even-numbered driving pixels are respectivelyobtained, are combined in alternating fashion, to acquire the peakpositions Xp′ at which the peak values P′(N) corresponding to all thedriving pixels are respectively obtained (step 3009).

Thereafter, the process returns to FIG. 12 and proceeds to step 1208,and the illuminance F(N) finally obtained based on P′(N) and Xp′ isstored in the light-amount storing memory 215 (step 1218). After that,the process proceeds to the flow of FIG. 16 where the shading correctionvalue is obtained based on the illuminance F(N). Here, as previouslydescribed, after obtaining the peak value P′(N) and the peak positionXp′ in accordance with the method of the present embodiment, the shadingcorrection value may be obtained by obtaining the illuminance F′(N) inaccordance with the method described in the second embodiment.

In the liquid crystal shutter array 118′ having the tilted drivingpixels shown in FIG. 9B, the driving pixels 234′ are arranged in asingle row, but the driving pixels may be arranged in a staggeredpattern. In that case, it is preferable that the odd-numbered drivingpixels be arranged along one row in the staggered pattern and theeven-numbered driving pixels along the other row in the staggeredpattern.

As the tilted driving pixels shown in FIG. 9B are used as describedabove, unexposed portions of the photosensitive material, which couldarise due to gaps between the driving pixels, can be prevented, makingit possible to prevent vertical stripes from being formed due to theunexposed portions remaining on the photosensitive material.Furthermore, by opening the odd-numbered driving pixels and theeven-numbered driving pixels separately in accordance with the flow ofFIG. 29, the peak value P′(N) and the peak position Xp′ can be obtainedaccurately.

1. A method for producing an exposure apparatus including an exposurehead having a plurality of light-emitting parts and a control means forcontrolling said exposure head, said method comprising the steps of:lighting said plurality of light-emitting parts at the same time;detecting an output light-amount distribution across all of saidplurality of light-emitting parts by making measurements using aline-like light-receiving device; detecting a peak positioncorresponding to each of said light-emitting parts by using said outputlight-amount distribution; detecting the amount of light of said eachlight-emitting part based on said each peak position; and determining,based on the amount of light of said each light-emitting part, acorrection value for correcting nonuniformity in the amount of light ofsaid each light-emitting part.
 2. The production method according toclaim 1, wherein said step of determining the amount of light of saideach light-emitting part includes the steps of: obtaining a valuecorresponding to said each peak position in said output light-amountdistribution; and determining said value as the amount of light of saideach light-emitting part.
 3. The production method according to claim 1,wherein said step of determining the amount of light of said eachlight-emitting part includes the steps of: providing a referencelight-amount distribution; obtaining a sole light-amount distributionfor said light-emitting part corresponding to said peak position, byusing said reference light-amount distribution and said outputlight-amount distribution near said peak position; and determining theamount of light of said light-emitting part based on said solelight-amount distribution.
 4. The production method according to claim1, wherein said light-emitting parts each have an opening tilted at aprescribed angle in a direction in which said light-emitting parts arearranged.
 5. The production method according to claim 4, wherein saidstep of lighting said plurality of light-emitting parts at the same timeincludes the steps of: lighting all of odd-numbered ones of saidplurality of light-emitting parts at the same time; and lighting all ofeven-numbered ones of said plurality of light-emitting parts at the sametime.
 6. The production method according to claim 5, wherein said stepof detecting said output light-amount distribution includes the stepsof: detecting a first output light-amount distribution occurring whenall of the odd-numbered ones of said plurality of light-emitting partsare lighted at the same time; and detecting a second output light-amountdistribution occurring when all of the even-numbered ones of saidplurality of light-emitting parts are lighted at the same time.
 7. Theproduction method according to claim 6, wherein said step of detectingsaid peak position includes the steps of: detecting a first peakposition by using said first output light-amount distribution; detectinga second peak position by using said second output light-amountdistribution; and combining said first peak position and said secondpeak position.
 8. The production method according to claim 1, whereinsaid control means has a memory, and is configured to control saidexposure head based on data stored in said memory, and wherein saidmethod further includes the step of storing said determined correctionvalue in said memory.
 9. The production method according to claim 1,wherein said light-receiving device includes light-receiving parts, eachhaving a width narrower than the width of each of said light-emittingparts.
 10. The production method according to claim 9, wherein thenumber of light-receiving parts contained in said light-receiving deviceis equal to an integral multiple of the number of said plurality oflight-emitting parts.
 11. The production method according to claim 10,wherein said light-receiving parts are arranged in such a manner thatthree or more light-receiving parts correspond to one light-emittingpart.
 12. The production method according to claim 9, wherein alight-receiving surface formed by said plurality of light-receivingparts is longer than a light-emitting surface formed by said pluralityof light-emitting parts.
 13. An exposure apparatus comprising: anexposure head having a plurality of light-emitting parts whose amountsof light each vary with a supplied driving signal; and a control means,having a memory, for generating said driving signal by correcting imagedata in accordance with a correction value stored in said memory,wherein said correction value is determined based on the steps of:lighting said plurality of light-emitting parts at the same time;detecting an output light-amount distribution across all of saidplurality of light-emitting parts by making measurements using aline-like light-receiving device; detecting a peak positioncorresponding to each of said light-emitting parts by using said outputlight-amount distribution; detecting the amount of light of said eachlight-emitting part based on said each peak position; and determining,based on the amount of light of said each light-emitting part, saidcorrection value for correcting nonuniformity in the amount of light ofsaid each light-emitting part.
 14. The exposure apparatus according toclaim 13, wherein said step of determining the amount of light of saideach light-emitting part includes the steps of: obtaining a valuecorresponding to said each peak position in said output light-amountdistribution; and determining said value as the amount of light of saideach light-emitting part.
 15. The apparatus according to claim 13,wherein said step of determining the amount of light of said eachlight-emitting part includes the steps of: providing a referencelight-amount distribution; obtaining a sole light-amount distributionfor said light-emitting part corresponding to said peak position, byusing said reference light-amount distribution and said outputlight-amount distribution near said peak position; and determining theamount of light of said light-emitting part based on said solelight-amount distribution.
 16. The exposure apparatus according to claim13, wherein said light-emitting parts each have an opening tilted at aprescribed angle to a direction in which said light-emitting parts arearranged.
 17. The exposure apparatus according to claim 16, wherein saidstep of lighting said plurality of light-emitting parts at the same timeincludes the steps of: lighting all of odd-numbered ones of saidplurality of light-emitting parts at the same time; and lighting all ofeven-numbered ones of said plurality of light-emitting parts at the sametime.
 18. The exposure apparatus according to claim 17, wherein saidstep of detecting said output light-amount distribution includes thesteps of: detecting a first output light-amount distribution occurringwhen all of the odd-numbered ones of said plurality of light-emittingparts are lighted at the same time; and detecting a second outputlight-amount distribution occurring when all of the even-numbered onesof said plurality of light-emitting parts are lighted at the same time.19. The exposure apparatus according to claim 18, wherein said step ofdetecting said peak position includes the steps of: detecting a firstpeak position by using said first output light-amount distribution;detecting a second peak position by using said second outputlight-amount distribution; and combining said first peak position andsaid second peak position.
 20. A production method to manufacture anexposure apparatus including an exposure head having a plurality oflight-emitting parts and a control means for controlling said exposurehead, said method comprising the steps of: lighting said plurality oflight-emitting parts at the same time; measuring amounts of light fromsaid plurality of light-emitting parts by using a light-receivingdevice; detecting a peak value and a peak position from measured valuesobtained by said light-receiving device; and determining, based on saidpeak value and said peak position, a correction value for correctingnonuniformity in the amount of light emitted from each light-emittingpart.